People with low levels of vitamin B12 may have a higher chance of getting Alzheimer's later in life, a study suggests.
Researchers discovered that the vitamin could protect against the disease by reducing levels of the amino acid homocysteine, which is found in the blood and has been linked to Alzheimer's.
The level of B12 that a person has varies, but it is generally lower for elderly people.
Non-dairy vegetarians may also suffer from low B12, as the vitamin is found in meat, fish and milk. Vitamin B supplements can be taken to combat this.
The study, which was conducted over seven years, looked at the blood samples from 271 Finnish people aged 65 to 79 who did not have Alzheimer's or any other form of dementia at the outset.
Blood samples were tested for levels of homocysteine, B12, and the active portion of the vitamin, called holotranscobalamin.
Each tiny step-increase in homocysteine concentration raised the risk of Alzheimer's by 16%.
But the risk was reduced by 2% every time levels of the active form of vitamin B12 went up.
The results were not affected by factors such as age, gender, education, smoking status, blood pressure and body mass index (BMI), a measurement of relative weight and height.
Study author Dr Babak Hooshmand, from the Karolinska Institute in Stockholm, Sweden, whose findings are reported in the journal Neurology, said: "Low levels of vitamin B12 are surprisingly common in the elderly. However, the few studies that have investigated the usefulness of vitamin B12 supplements to reduce the risk of memory loss have had mixed results."
"The link between untreated B12 deficiency and dementia has been known for a number of years. Blood tests in the elderly should include B12 levels, although the test itself may be flawed as it cannot distinguish between active and inactive B12. Of course this disease is not confined to the elderly, myself having the hereditary form of PA. My elderly mother has dementia and her low levels were not picked up until after I was diagnosed and requested her to be tested. More importance should be made on earlier diagnosis for the deficiency, maybe lives will be improved" - Caroline Stephens, Scotland